Ethanol, C2H5OH, melts at -114°C and boils at 78°C.?

Question

The enthalpy of fusion of ethanol is 5.02 kJ/mol, and its enthalpy of vaporization is 38.56 kJ/mol. The specific heats of solid and liquid ethanol are 0.97 J/gK and 2.3 J/gK, respectively. How much heat is required to convert 62.0 g of ethanol at -135°C to the vapor phase at 78°C? Please, if anyone can figure this out, thank you so very much.

Answer 1

Step 1. Convert temperature to Kelvin since your specific heat capacities uses Kelvin as in joules per gram per Kelvin.

Step 2. Convert the enthalpies to joules since once again the specific heat capcities uses joules as in joules per gram per Kelvin.

Step 3. Get the molecular weight of ethanol in g/mol.

The trick is to avoid the mismatch in the units before applying the formulas. People get burned by the mismatch. Even if the numbers end up right and the units matched up at the very end, professors sometimes still take points away if the units didn't match up correctly somewhere in the solution.

So formula would look something like this:

total energy = (mass of ethanol) * (solid specific heat) * (T-Melt - T-initial) + (mass of ethanol) /(molecular weight in g/mol) * (enthalpy of fusion) + (mass of ethanol) * (liquid specific heat) * (T-Boil - T-Melt) + (mass of ethanol) / (molecular eight in g/mol) * (enthalpy of vaporization).


T-Melt is the melting point in Kelvin. You know it as -114 degrees C.

T-Initial is the initial temperature in Kelvin (-135 degrees C).

Etc. ..

Just plug in the values. The unit of measure would be in joules.

Answer 2

Firstly calculate the molecular weight of ethanol from the atomic weights of constituents:
carbon 12x2=24
hydrogen 1x6=6
oxygen 16x1=16
total 46 g/mole

Next to heat the solid ethanol from -135C to -114C ie by 21C or 21K requires:
21 x .97 x 62/1000 = 1.26 kJ

Then to melt the ethanol at -114C requires:
5.02 x 62/46 = 6.77 kJ

To raise the temperature of the liquid ethanol from -114C to 78C ie by 192C or 192K requires:
192 x 2.3 x 62/1000 = 27.38 kJ

To vapourise the ethanol requires:
38.56 x 62/46 = 51.97 kJ

Total heat required = 1.26 + 6.77 + 27.38 + 51.97 = 87.38 kJ

Answer 3

Step a million: good at -a hundred thirty five to good at -114. Use particular warmth of robust. Step 2: good at -114 to liquid at -114. Use enthalpy of fusion Step 3: liquid at -114 to liquid at seventy 8. Use particular warmth of liquid Step 4: liquid at seventy 8 to vapor at seventy 8. Use enthalpy of vaporization completed. Do your very own math.